We’re in speculation-ville here, so don’t take this all too seriously yet. The short answer to the headline’s question: probably not in a huge way. Mission: Impossible is an established franchise with an audience base and an appeal that goes beyond Tom Cruise, so even if Cruise’s action comedy Knight and Day doesn’t find an audience, the prospects for Mission: Impossible 4 shouldn’t be ruled out.

But with a new draft of the script in hand at Paramount and the final green light decision approaching, there’s a speculative report that Paramount is thinking hard about how to approach the fourth film in the super-spy franchise.

Deadline reports that continued concerns about the viability of Tom Cruise as a mega-budget action star in 2010 are nagging at Paramount as Cruise’s Knight and Day opens today to tracking numbers that have been far less than enthusiastic.

Josh Applebaum and Andre Nemec have just turned in their script for MI4, and Deadline says that Paramount’s Brad Grey and Rob Moore are going to spend the next couple days reading the draft and figuring out the budget for the film to be directed by Brad Bird. So the question is: as returns from Knight and Day come in over the same time period, will that have an effect on MI4?

As Deadline notes, there’s not much chance that Paramount would scrap the film, even if Knight and Day tanks. There’s also probably little room to significantly lower the budget, given that there are three previous films against which this sequel will be compared. There are a few reasons to carry on with MI4: extensive money already spent on development, the clout of producer JJ Abrams, and the studio’s attachment to Cruise in the wake of the Les Grossman movie deal.

The intriguing notion presented by the report is to turn MI4 into a two-hander — that is, to emphasize a subplot involving a junior operative so that the film effectively becomes about a pair of agents, one of whom (obviously) isn’t Tom Cruise. (Think of how MI3 might have been changed had the arc of Keri Russell‘s character been given greater prominence.) Doing that, the studio gets to keep the franchise, but has a non-Cruise marketing hook on which to hang the film.